debit notes/invoice

could any one pls clarify on below points:

1.if sales bills/invoices/Debit notes raised to party but pending to account in fy17-18 so exactly now in which month to book that sales ..

2. if party raise bill in March and found in gst2a, but itc credit not taken yet , so in which month to book that purchase bill and wen to take that credit and how..